Electrophotographic imaging systems involve the formation and development of electrostatic latent images on the surface of photoconductive devices referred to in the art as photoreceptors. In these imaging systems, a photoreceptor containing a photoconductive insulating layer is imaged by uniformly electrostatically charging its surface. The photoreceptor is then exposed to a pattern of activating electromagnetic radiation such as light, thereby selectively dissipating the charge in the illuminated areas, causing a latent electrostatic image to be formed in the non-illuminated areas. This latent electrostatic image can be developed with developer compositions containing toner particles, and the developed image can be transferred to a suitable substrate such as paper.
Many known photoconductive members can be selected for incorporation into the electrophotograhic imaging system including, for example, photoconductive insulating materials deposited on conductive substrates, as well as those containing a thin barrier layer film situated between the substrate and the photoconductive composition. The barrier layer is primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer subsequent to charging, as injection could adversely affect the electrical properties of the photoconductive compositions involved.
An electrophotographic imaging member may be provided in a number of forms. The imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. Examples of photoconductive members include those comprised of inorganic and organic materials, layered devices comprised of inorganic or organic compositions, composite layered devices containing photoconductive substances dispersed in other materials, and the like.
U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
As more advanced higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor may also comprise additional layers such as an optional anti-curl back coating and an optional overcoating layer.
Examples of known photogenerating materials include trigonal selenium and various phthalocyanines. Examples of known hole transport materials include certain diamines dispersed in inactive polycarbonate resin materials.
A polycarbonate is a synthetic thermoplastic resin which can be formed from a dihydroxy compound and a carbonate diester or diacid. A common polycarbonate is derived from bisphenol A (2,2-bis(4-hydroxyphenol)propane) and phosgene. Polycarbonate polymers based on bisphenol A have been used as the binder for the hole transport molecule N,N'-diphenyl-N,N'-bis-5-methylphenyl-[1,1'biphenyl]-4,4'-diamine in photoreceptors. Other layers of a photoreceptor may also use polycarbonates as a binder material.
U.S. Pat. No. 4,835,081 to Ong et al. discloses an imaging member comprised of a photoconductive layer, and a protective electron transport polymer overcoating having the formula: ##STR1## wherein A is a trivalent linkage, B is a functional group such as an ester (--OCO--), carbonate (--OCOO--), or carbamate (--OCONH--); and R is a bivalent linkage, and wherein n represents the number of repeating units, for example, from about 25 to about 300. The polymer overcoating may be synthesized by polycondensation of a bisphenol with a bishaloformate, phosgene, a dialkyl or diaryl carbonate Examples of bishaloformates that may be employed for the polymerization include ethylenegylcol bischloroformate, propyleneglycol bischloroformate, butyleneglycol bischloroformate, diethyleneglycol bischloroformate, triethyleneglycol bischloroformate, and the like. The polymerization can be effected either by melt polymerization under reduced pressure in the presence of a catalyst or by solution polymerization, depending on the nature of reagents used. For example, polycondensation of a functionalized bisphenol and an aliphatic bischloroformate is conducted in a suitable solvent at 10.degree.-30.degree. C. in the presence of a base such as pyridine.
U.S. Pat. Nos. 4,937,165 and 5,011,906, both to Ong et al., disclose a layered photoconductive imaging member comprised of a photogenerating layer comprised of organic or inorganic photoconductive pigments optionally dispersed in an inactive resinous binder and situated between a supporting substrate and a charge transport layer containing N,N-bis(biarylyl)aniline charge transport polymers, optionally doped with a suitable charge transport compound and/or optionally dispersed in a resin binder such as a polycarbonate ##STR2## where A is a bifunctional linkage such as O, alkyleneoxy with from about 1 to about 20 carbon atoms such as OCH.sub.2, OCH.sub.2 CH.sub.2, OCH.sub.2 CH.sub.2 O and the like; B is a bifunctional linkage such as COR'--'CO, COOR"OCO, CONHR'--'NHCO, wherein R" is an alkylene function with from about 1 to about 10 carbon atoms such as methylene, dimethylene, trimethylene, 3,3-dimethylpentamethylene, and the like, an arylene function with from about 6 to about 24 carbon atoms such as phenylene, phenylene, tolylene, anisylene, biphenylene, and the like, ether, or polyether segments, such as CH.sub.2 C--H.sub.2 OCH.sub.2 CH.sub.2, (CH.sub.2 CH.sub.2 O).sub.2 CH.sub.2 CH.sub.2, C.sub.6 --H.sub.4 OC.sub.6 H.sub.4 and the like; Z is alkylenedioxy, arylenedioxy or substituted derivative thereof with 1 to 24 carbon atoms such as 1,3-trimethylenedioxy, 1,4-tetramethylenedioxy, 1,6-hexamethylenedioxy, 1,4-phenylenedioxy, bis(oxyphenyl) propane, bis(oxyphenyl) methane, bis(oxyphenyl)cyclopropane, and the like; and R and R' are substituents such as alkyl, alkoxy, with 1 to about 25 carbon atoms such as methyl, ethyl, propyl, methoxy, ethoxy, propoxy, aryl, or aryloxy such as phenyl, tolyl, phenoxy, and the like, and a halogen such as chlorine, bromine, and the like. The charge transporting N,N-bis(biarylyl)aniline polymers or copolymers can be readily synthesized from the corresponding bifunctionalized monomers such as the corresponding dihydroxy derivatives by polycondensation with suitable bifunctional reagents. The latter can be selected from the group consisting of diacyl halide such as succinyl chloride, adipoyl chloride or azelaoyl chloride, bishaloformates such as ethylene glycol bischloroformate, propylene glycol bischloroformate, or diethylene glycol bischloroformate, and diisocyanates such as hexane diisocyanate, benzene diisocyanate or toluene diisocyanate. Also, the charge transport copolymers can be obtained by copolymerization, for example, with suitable dihydroxy comonomers, such as bisphenol A, bisphenol Z, and other similar diols.
U.S. Pat. No. 4,959,288 to Ong et al. discloses a photoresponsive imaging member comprised of a charge transporting diaryl biarylylamine copolymer situated between a supporting substrate and a photogenerating layer. The charge transporting diaryl biarylylamine copolymers can be readily synthesized by the copolycondensation of stoichiometric quantities of a bifunctionalized monomer such as the corresponding dihydroxy derivatives and a suitable dihydroxy comonomer such as bisphenol A, bisphenol Z, and other similar bisphenols, with appropriate bifunctional reagents. The latter can be selected from the group consisting of diacyl halide such as adipolyl chloride, bishaloformates such as ethylene glycol bischloroformate or diethylene glycol bischloroformate, and diisocyanates such as benzene diisocyanate, toluene diisocyanate, and the like.
Traditional methods of manufacturing polycarbonate polymers usually involve the use of phosgene, which is a highly toxic substance, and/or high temperatures.
U.S. Pat. No. 4,369,303 to Mori et al. discloses a process for preparing an aromatic polyesterpolycarbonate comprised of a dihydroxydiaryl compound, a terephthaloyl chloride and/or isophthaloyl chloride reactant, and phosgene. The aforementioned reactants are polycondensed in the presence of water, methylene chloride and an acid binding agent thereby producing the polycarbonate through an interfacial polymerization process.
U.S. Pat. No. 4,722,994 to Boden discloses a method of producing cyclic oligomeric polycarbonates from the reaction of dihydric phenols and carbonyl halides, involving an interfacial polymerization reaction of the disodium salt of bisphenol-A, a triethylamine polymerization catalyst and methylene chloride with phosgene.
U.S. Pat. No. 4,902,758 to Marks discloses a process for synthesizing high molecular weight segmented block copolycarbonates utilizing an interfacial polymerization reaction. Such polycarbonates may be prepared sequentially from diphenols and tetrahalogenated diphenol.
Many polycarbonate polymers have a limited life span. Efforts to find more durable polymers have been based on melt polycondensation or the use of toxic phosgene gas to produce novel polycarbonate structures.
Polycarbonate polymers based on bisphenol A have been used as a binder for hole transport layers in photoreceptors. Since the introduction of the first products using such photoreceptors, there has been an ongoing effort to find a replacement for these polymers which will extend the life of the photoreceptor. Most of these methods involved the use of toxic phosgene gas to make these polycarbonates. Melt polycondensation offers a number of attractive features in producing polycarbonates, such as avoidance of using phosgene and solvents. However, a number of drawbacks to this process also exist. Due to the high temperatures associated with melt polycondensation, only monomers which can withstand these temperatures can be incorporated into the polycarbonate structure. This limits the structures of the polycarbonates which can be used and makes the incorporation of specialty monomers into the backbone very difficult. The ability to make co-polymers, random as well as alternating, via melt polycondensation is also limited. Due to the high viscosities of polycarbonates, very specialized equipment operating at high temperatures is required to carry out these reactions.